I am always a little leary when I tell the waitress the steak is to rare and she has to take it back. I have heard terrible tales as to what the cook does when it is brought back because he don't like his cooking questioned.
I would think that they should be mature enough to not hold a grudge just b/c you wanted it a little more cooked! (Unless of course when you sent it back, you said, "Please kill it before serving it to me!" lol)
Not only that I've seen it on one of those hidden camera programs and it wasn't pretty. It does makes you appreciate that home cooked food a lot more.